Figure 2.

Estimates of gene expression levels for three yeast transcription factors after 30
minutes of exposure to 7% vol/vol ethanol during peak growth phase. (a) Likelihood contour plots for the relative gene-expression level () and experimental error variance (2). For each gene, surfaces have a single peak. (b) Credible intervals for gene-expression level for three yeast transcription factors
that are candidates for the ethanol shock response, taken from cultures at log-phase
growth either unexposed or exposed to 30 min of 7% v/v ethanol. Because the slope
of the likelihood is much steeper to the right than to the left of this ridge represented
in (a), credible intervals with two-sample data such as this are highly asymmetric.
More balanced experimental designs have more symmetric credible intervals. Using a
conservative gene-by-gene criterion of nonoverlapping 95% credible intervals, none
of these transcription factors shows statistically significantly differential gene
expression, although GCR1 is close. MSN4 is the gene for a zinc-finger transcriptional activator for genes regulated through
Snf1p. A general regulator for stress response, it does not seem to be responsible
for upregulation of stress genes in response to ethanol. HSF1 is the gene for a heat-shock transcription factor that binds to the heat-shock DNA
element at both normal and elevated temperatures. Although the difference in estimates
observed here is suggestive of regulatory action of the heat-shock response, these
differences are not statistically significant. GCR1 encodes a positive regulator of glycolytic genes, including GLK1. Although the difference in estimates observed here is suggestive of regulatory action
on transcription of transposable elements and the trehalose pathway, the differences
are not statistically significant by a conservative criterion of nonoverlapping 95%
credible intervals.